A Numerical Modeling Study Of The Circulation And Plankton Ecosystem Dynamics Of The Bohai Sea

With higher spatial resolution of 2'X2' longitude-latitude grid, circulation in the Bohai Sea is investigated with a three-dimensional baroclinic model-HAMSOM (HAMburg Shelf Ocean Model). Most affecting factors such as tide, wind, thermohaline and river discharge are concerned, and the dominant factors in different seasons are indicated. Circulation through the Bohai Strait is discussed in focus. In the mean time, water temperature of the Bohai Sea during 1998 to 1999 is simulated in forecasting mode. For the reason of low resolution of meteorological data, calculation of surface latent heat flux is perfected by using historical evaporation data, and the bug of heat budget nearshore is improved on.The results show that circulation in the Bohai Sea is weak, mainly affected by tide, wind, thermohaline and river discharge, in which the last mainly affect the south part of the Bohai Sea. In different seasons and weather conditions, the dominant affecting factors are different too. Tidal residual circulation always exists and is steady; in the long term it is the main contributor to the general circulation. The character of seasonal circulation is as follows: wind-driven circulation and tidal residual circulation dominate in winter (February); wind-driven circulation, tidal residual circulation and thermohaline circulation dominate in spring (May); tidal residual circulation and river discharge dominate in summer, the influence of wind stress is significant in Liaoxi coastal area, and Huanghe river discharge plays an important role in the estuary; in autumn four factors are all significant.In different seasons, water exchange between the Bohai Sea and the Huanghai Sea through the Bohai Strait is different in some extent. In spring, water of the Huanghai Sea flow into the Bohai Sea through south of the Strait, and water of the Bohai sea flow out through the north part of the strait; in other three seasons the condition is in contrary. Additionally, a remarkable character is that in the north part of the Strait there is always a dipole, which flows inward in the north and flows outward in the south. The reason of the dipole coming into being is the joint-action of tide and terrain.On the basis of HAMSOM, a three-dimensional plankton ecosystem dynamics NPZD model is constructed with proper biological functions and variables. With this model, plankton ecosystem of the Bohai Sea in 1999 is investigated. Considering the notable difference between simulation and survey in winter, the death functions of phytoplankton and zooplankton are perfected in this paper, which is proved to be effective later.The results indicate that the annual variation of phytoplankton biomass in most area of the Bohai Sea is double-peaked. The concentration of chlorophyll-a is about 0.2mg/m3 in winter, when is the lowest period in a year. Algae bloom breaks out in spring and the concentration of chlorophyll-a could reach 6mg/m3, when is the highest period in a year; the duration of spring algae bloom is about half a month. In summer, the concentration of chlorophyll-a is lower than in spring; algae bloom break out again in August and September, the duration of autumn algae bloom is longer than 1 month.The variation of phytoplankton is not the same in different area of the Bohai Sea. In themiddle of the Bohai Sea, algae bloom breaks out in spring and autumn, while in Bohai Bay and Liaodong Bay the bloom breaks out mainly in summer, and in Laizhou Bay the variation of phytoplankton is consistent with that of the runoff of Huanghe river.In the middle of the Bohai Sea, the vertical distribution of phytoplankton is affected by thermocline in July and August; the concentration is high in middle layers and low in upper and lower layers, or high in middle and lower layers and low in upper layers. Influence of thermocline is more remarkable in offshore area, while in nearshore area the water is shallow and mixed well, and phytoplankton is almost equally distributed in vertical.The influence of circulation on plankton ecosystem of the Bohai Sea is...